This is an issue that will occur when the map is added to a spry tabbed panel.
To fix the problem, find the following line of code in the google_javascript/wagmp_map_1.js file:
var map = new GMap2(document.getElementById('wagmp_map_1'));
to:
var mapElem = document.getElementById('wagmp_map_1');
var mapWidth = mapElem.style.width;
var mapHeight = mapElem.style.height;
var map = new GMap2(document.getElementById('wagmp_map_1'),{size:new GSize(mapWidth.replace('px',''),mapHeight.replace('px',''))});
